Is this a competition kettlebell or a regular gym bell?

It is built to competition spec, with a 35 mm handle and uniform steel body. That makes it suited to kettlebell sport rather than general cast-iron gym use.

What does 35 mm mean for my grip?

35 mm is the competition-standard handle diameter, thicker than most cast-iron bells. Lifters with smaller hands may find it harder to hold for long sets.

Is it hollow or filled?

It is gravity cast from pure steel with no fillers, so the body is solid steel rather than a shell packed with material.

Does the handle work for two-hand swings?

The 35 mm handle is wide enough for two-hand swings, though competition bells are mainly designed for one-arm sport lifts.

How does it compare with cast-iron kettlebells?

It has a uniform competition shape and a steel handle instead of a painted cast-iron finish. That consistency costs more than a typical cast-iron bell.